Q: Mac Pro 3,1 will not boot with both memory riser cards installed

So I am wondering if anyone has had a similar problem and here it is:

1. My Mac Pro 3,1 2008 will not power on with both memory riser cards seated (or more accurately will rarely boot with both memory riser cards seated)
2. Both memory riser cards are full with RAM.  Both memory riser cards will work if installed by itself but the Mac will not power on if both are installed
3. I have tried taking all of the RAM out of one of the memory riser cards that does not seem to help

Anybody have any ideas on this? Faulty Power Supply?